1. Field of the Invention
The present invention relates to a method for producing a light reflective film having a light reflective laminate film that includes plural layers each having a cholesteric liquid crystal phase fixed therein, especially to a method for producing such a light reflective film to be stuck to windows of buildings, car windows, etc. The invention also relates to the light reflective film produced according to the production method of the invention.
2. Description of the Related Art
Recently, with the increase in the interest in environment and energy, the needs for energy-saving industrial products are high, and as one of them, glass and films are desired that are effective for heat shields for windowpanes in houses, cars and the like, or that is, for reducing thermal load from sunlight through windowpanes. For reducing the thermal load from sunlight, it is necessary to prevent transmission of the sun's rays in any of the visible range or IR range of the sunlight spectrum. In particular, for car windows, high transmittance in the visible light range is desired from the viewpoint of safety, and the need for heat shielding is also high, and in some countries, there is a tendency to regulate solar reflectance.
Double glass coated with a particular metal film capable of shielding against thermal radiation, which is called low-E pair glass, is well used as eco-glass having high heat insulating/shielding capability. The particular metal film may be formed, for example, by laminating plural layers according to a vacuum film formation method. The particular metal film coating to be formed through vacuum film formation is extremely excellent in reflectivity, but the vacuum process is nonproductive and the production cost thereof is high. In addition, the metal film, when used, concurrently shields against electromagnetic waves, and is therefore problematic in that, when used in mobile phones and the like, it causes radio disturbance, and when used for automobiles, ETC could not be used therein. Not only solving the problem of radio disturbance but also high transmittance of visible light is desired for car windows from the viewpoint of safety.
A method of using a cholesteric liquid crystal phase in a light reflective film has been proposed. For example, as disclosed in Japanese Patent 4109914, by forming one cholesteric liquid crystal layer on both sides of a λ/2 plate, a light circularly-polarized in one direction can be selectively and efficiently reflected within a range of from 700 to 1200 nm.
JP-T 2009-514022 discloses an IR-reflective article having a cholesteric liquid crystal layer. Regarding lamination of plural cholesteric liquid crystal layers, there have been made various attempts to use the laminate in liquid crystal display devices, and concretely, there are known various approaches to a technique of efficiently reflecting light in a visible light region; and for example, Japanese Patent 3500127 discloses a case of lamination of multiple cholesteric layers. In Examples in Japanese Patent 3500127, a step of applying a cholesteric liquid crystal material to an alignment film-coated glass substrate followed by curing it thereon is repeated to produce the intended laminate.
Japanese Patent 4008358 discloses a method for producing a broadband cholesteric liquid crystal film through UV-polymerization of a predetermined liquid crystal mixture between two substrates. However, there is given no concrete description relating to a method for producing a laminate film including plural layers. Japanese Patent 3745221 discloses a circularly-polarized light extracting optical device in which plural liquid crystal layers each formed of three-dimensionally crosslinked liquid crystal molecules having cholesteric regularity are laminated under a predetermined condition. In Examples in Japanese Patent 3745221, a coating liquid of a liquid crystal material is applied onto a glass substrate in a mode of spin coating and thereafter the liquid crystal molecules are three-dimensionally crosslinked through irradiation with light to form the constitutive layers, thereby producing a laminate-structured device.
JP-A 2002-22960 discloses a case of configuration having an antistatic light-diffusive layer formed on one side or both sides of a cholesteric layer. JP-A2004-252257 discloses a case of configuration having an antistatic layer formed by applying an antistatic agent to the surface and/or the back of a light-diffusive sheet.